Previous images of this area by other space missions indicate that this is a shield volcano with very shallow slopes. What HiRISE reveals is that it is completely covered by a blanket of dust.
While volcanic features remain obscure, the dust does exhibit some very strange patterns. As you zoom into the middle of the image, the ground appears covered with a fine network of light and dark polygons. But at full resolution, it can be seen that these polygons are actually the edges of small scallops.
The dust is apparently held together by some unknown means, giving it sufficient strength to be carved into this strange pattern.
Written by: Laszlo P. Kestay (9 June 2010)
More info and image formats at http://hirise.lpl.arizona.edu/PSP_001840_1660
Image: NASA/JPL/University of Arizona